ecdsautils is a tiny collection of programs used for ECDSA (keygen, sign, verify). "ecdsa_verify_[prepare_]legacy()" does not check whether the signature values "r" and "s" are non-zero. A signature consisting only of zeroes is always considered valid, making it trivial to forge signatures. Requiring multiple signatures from different public keys does not mitigate the issue: "ecdsa_verify_list_legacy()" will accept an arbitrary number of such forged signatures. Both the "ecdsautil verify" CLI command and the libecdsautil library are affected. The issue has been fixed in ecdsautils 0.4.1. All older versions of ecdsautils (including versions before the split into a library and a CLI utility) are vulnerable.